Process and apparatus for vaporizing liquefied natural gas

ABSTRACT

THE PRESENT INVENTION RELATES TO AN IMPROVED PROCESS AND APPARATUS FOR VAPORIZING LIQUEFIED NATURAL GAS WITH TURBINE EXHAUST GASES WHEREIN THE VAPORIZED NATURAL GAS IS PASSED THROUGH HEAT EXCHANGE TUBES IN A HEAT EXCHANGER FOR COOLING THE INPUT AIR TO THE TURBINE. A STREAM OF LIQUEFIED NATURAL GAS IS VAPORIZED AND HEATED WITH THE TURBINE EXHAUST GASES TO A TEMPERATURE WHICH WILL BRING ABOUT THE FORMATION OF A MINIMUM QUANTITY OF ICE ON THE OUTSIDE SURFACES OF A FIRST BANK OF SAID HEAT EXCHANGE TUBES, AND IS PASSED THROUGH SAID FIRST BANK OF HEAT EXCHANGE TUBES TO COOL THE TURBINE INPUT AIR. A SECOND STREAM OF LIQUEFIED NATURAL GAS IS THEN COMBINED WITH THE VAPORIZED NATURAL GAS STREAM TO COOL THE RESULTING COMBINED STREAM TO A TEMPERATURE WHICH WILL BRING ABOUT   THE FORMATION OF A MINIMUM QUANTITY OF ICE ON THE OUTSIDE SURFACES OF A SECOND BANK OF SAID HEAT EXCHANGE TUBES. THE COMBINED STREAM IS THEN PASSED THROUGH THE SECOND BANK OF HEAT EXCHANGE TUBES SO THAT THE TURBINE INPUT AIR IS COOLED FURTHER. AS MANY ADDITIONAL BANKS OF HEAT EXCHANGE TUBES MAY BE PROVIDED AS ARE REQUIRED TO COOL THE AIR TO A DESIRED TEMPERATURE, AND THE STREAM OF NATURAL GAS RECOOLED WITH ADDITIONAL STREAMS OF LIQUEFIED NATURAL GAS IN THE MANNER DESCRIBED ABOVE BEFORE IT ENTERS EACH BANK.

Jim 5, 1971 E. M.ARENsoN Y 3,552,134

PROCESS AND APPARATUS FOR'VAPORIZING LIQUEAFIED NATURAL GAS n. y u mw /WNw M/ n n E N IMU d MH WW W Lb I 7 M. W .J S v 2 QM W l M mwm S M NT muGQ and S A @n v @Sunni A Tmw Y d Y u s d u u u w QQ \.& u M v auf EN Awn) 3 e .0V t Q lV w m26 k NX S QT L l Q hmkm. ,%.\\r\ n 0% f w \Q1 Si fQQQ QM Q .m .w n QT- SR J A d .n

Jan. 5, 1971 E. M.-ARENsoN 3,552,134

PROCESS AND APPARATUS FOR `VPORIZING LIQUEFIED NATURAL GAS Filed July22, 1969 v v 2 sheets-sheet z United States Patent Ofice 3,552,134Patented Jan. 5, 1971 PROCESS AND APPARATUS FOR VAPORIZING LIQUEFIEDNATURAL GAS Edwin M. Arenson, El Reno, Okla., assignor to Black,

Sivalls & Bryson, Inc., Oklahoma City, Okla., a corporation of DelawareFiled July 22, 1969, Ser. No. 843,413 Int. Cl. F17c 7/02, F02m 3l /00U.S. Cl. 62-53 14 Claims ABSTRACT OF THE DISCLOSURE The presentinvention relates to an improved process and apparatus for vaporizingliquefied natural gas with turbine exhaust gases wherein the vaporizednatural gas is passed through heat exchange tubes in a heat exchangerfor cooling the input air to the turbine. A stream of liquefied naturalgas is vaporized and heated with the turbine exhaust gases toa'temperature which will bring about the formation of a minimum quantityof ice on the outside surfaces of a first bank of said heat exchangetubes, and is passed through said first bank of heat exchange tubes tocool the turbine input air. A second stream of liquefied natural gas isthen combined with the vaporized natural gas stream to cool theresulting combined stream to a temperature which will bring about theformation of a minimum quantity of ice on the outside surfaces of asecond bank of said heat exchange tubes. The combined stream is thenpassed through the second bank of heat exchange tubes so that theturbine input air is cooled further. As many additional banks of heatexchange tubes may be provided as are required to cool the air to adesired tempertaure,` and the stream of natural gas recooled withadditional streams of liquefied natural gas in the manner describedabove before it enters each bank.

BACKGROUND OF THE INVENTION (l) Field of the invention The presentinvention relates generally to an improved process and apparatus forvaporizing liquefied natural gas, and more particularly, but not by wayof limitation, to a process and apparatus for vaporizing liquefiednatural gas with turbine exhaust gases wherein the turbine input air iscooled in stages with a strea/m of the vaporized natural gas. The streamof vaporized natural gas is maintained at a temperature level which willbring about the formation of a minimum quantity of ice within theapparatus.

(2) Background of the invention Liquefed natural gas is normallyvaporized by the addition of heat to return into its natural gas statefor use. For instance, natural gas may be liquefied and stored toprovide gas for short periods of time during which demands areexcessively high. This stored liquefied natural gas is at a temperatureof 258 F., and must be heated in order to vaporize it and return it toits normal state for use.

A conventional turbine of the type used to generate electric powerconsumes enonmous quantities of air and generates large volumes of veryhot exhaust gases. 'The horsepower output of the turbine may beincreased by cooling the turbine input air.

Various processes have been proposed for vaporizing liquefied naturalgas with turbine exhaust gases wherein the liquefied natural gas is usedto cool the turbine input air. Also, processes hafve been proposedwherein the liquefied natural gas is rfirst vaporized with turbineexhaust gases, and then used to cool the turbine input air. Theseproposals have merit in that facilities embodying such processes may beused to both generate electricity and vaporize liquefied natural gasmore economically than can separate facilities. However, a problem isencountered when it is attempted to cool turbine input air withliquefied natural gas in conventional heat exchange apparatus in thatice will form in the apparatus due to water vapor condensing andfreezing therein. That is, liquefied natural gas at a temperature of 258F. will cause the outside surfaces of heat exchanger tubes to have atemperature well below the temperature at which water vapor inatmospheric air will condense and freeze. Continued operation of such aheat exchanger will result in the formation of layers of ice within theheat exchanger until the pressure loss of the air passing through theheat exchanger is excessive, of the air flow is completely blocked olfby the ice in the heat exchanger.

Also, it has been found that a similar problem exists when it isattempted to cool turbine input air with a stream of vaporized naturalgas. Since it is desirable to reduce the turbine input air fromatmospheric conditions to a temperature of 30 F. to 40 F., if it isattempted to use vaporized natural gas to cool the air in a single stageof heat exchange, the vaporized natural gas must be at a temperaturewell below the condensing and freezing point of water vapor. Therefore,ice |will form in the heat exchange apparatus used in the same manner asdescribed above.

The present invention is directed to an improved process and apparatusfor vaporizing liquefied natural gas with turbine exhaust gases andcooling the turbine input air with the vaporized natural gas wherein theturbine air is cooled in two or more stages with a minimum of ice formedin the heat exchange apparatus used.

SUMMARY OF THE lINVENTION The present invention is directed to a processfor vaporizing a stream of liquefied natural gas with turbine exhaustgases wherein vaporized natural gas is passed through heat exchangetubes in heat exchange relationship with the input air of the turbinethereby cooling the input air. A first stream of liquefied natural gasis vaporized and heated with turbine exhaust gases to a temperaturewhich will bring about the formation of a minimum quantity of ice on theoutside surfaces of the heat exchange tubes. The stream of vaporizednatural gas is then passed through a first bank of the heat exchangetubes so that the turbine input air is cooled and the vaporized naturalgas stream is heated. A second stream of liquefied natural gas is thencombined with the streai of vaporized natural lgas so that the combinedstream.- is cooled to said temperature and the second stream ofliquelied natural gas is vaporized. The combined stream is then passedthrough a second bank of heat exchanger tubes so that said turbine inputair is cooled further, and the combined stream is removed from theprocess. Apparatus is also provided by the present invention.

It is, therefore, a general object of the present invention to providean improved process and apparatus for vaporizing liquefied natural gas.

A further object of the present invention is the provision of a processand apparatus for vaporizing liquefied natural gas with turbine exhaustgases wherein the vaporized natural gas may be used to cool the turbineinput air.

Yet a further object of the present invention is the provision of animproved process and apparatus for cooling turbine input air withnatural gas vaporized with the turbine exhaust gases wherein a minimumquantity of ice is formed on the outside surfaces of heat exchange tubesused to cool said turbine input air.

Still a further object of the present invention is the provision ofrelatively inexpensive apparatus for vaporizing liquefied natural gaswith turbine exhaust gases and cooling the turbine input air with saidvaporized natural gas wherein a minimum of ice will form in saidapparatus an excessive pressure loss or stoppage of the air will notresult.

Other objects and advantages of the invention will be evident from thefollowing detailed description when read in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. l is a view of apparatus forcarrying out the process of the present invention in diagrammatic form.

FIG. 2 is a side elevational view of the apparatus of the presentinvention, and

FIG. 3 is a top view, partially in section, of the apparatus of FIG. l.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawingsand particularly to FIG. o

l, a stream of atmospheric air is drawn through conduit into an aircooler 12. Air cooler 12 basically comprises a plurality of heatexchange tubes 14 for cooling the air passing therethrough. The cooledair passes out of air cooler 12 through conduit 16 into a conventionalturbine 18. Turbine 18 is of the type wherein large quantities of airare mixed with natural gas and combusted thereby generating largevolumes of hot exhaust gases. The exhaust gases from such a turbine willnormally be at temperatures in the range of from 900 F. to 1000 F.

Turbine 18 is used to operate a conventional electric generator 20. Thehot combustion gases from turbine 18 pass through conduit 22 into aliquefied natural gas heater 24. From heater 24 the exhaust gases passthrough conduit 26 from where they may be vented to the atmos- K phere.

A stream of liquefied natural gas stored in storage tank 28 is pumpedthrough conduit 30 into conduit 32 by a conventional pump 34. Aconventional hand-controlled throttling-type valve 36 is disposed inconduit 32, and a conduit 38 is connected to conduit 32 upstream ofvalve 36. As will be described further herein valve 36 is adjusted sothat a portion of the liquefied natural gas pumped by pump 34 passesinto conduit 38. The major portion of the liquefied natural gas streampasses through valve 36 and conduit 32 into a bank 40 of heat exchangertubes 2S, connected in series, and disposed within heater 24. Theliquefied natural gas passing through heat exchanger tube bank 40 isvaporized and heated to a desired temperature by the turbine exhaustgases passing on the outside of heat exchanger tubes 25. The vaporizedand heated natural gas is conducted from heater 24 through conduit 42.

A conventional temperature controller 44 is connected to conduit 42 tosense the temperature of natural gas passing therethrough. Temperaturecontroller 44 may be any pneumatic or electric temperature controllerwhich will generate a signal proportional to the deviation of thetemperature sensed from a selected temperature. A bypass conduit 46 isattached to conduit 42 and to conduit 32. A conventional control valve48 is disposed within conduit 46 which may be any conventional automaticcontrol valve which will open and close in response to the signalgenerated by temperature controller 44.

Conduit 42 is connected to a tirst bank 50 of heat exchange tubes 14connected in series and disposed within air cooler 12. Vaporized naturalgas conducted to heat exchange tube bank 50 by conduit 42 passes throughbank 50 thereby cooling the air passing on the outside of bank 50. Thevaporized natural gas, which is heated while passing through heatexchanger tube `bank 50, passes into a header 88 which is connected toheader 98.

Conduit 38 is connected to conduit 54 which is in turn connected toheader 98. A conventional control valve 56 is disposed within conduit54. A portion of the liquefied natural gas stream passing throughconduit 38 passes through conduit 54, control valve 56 into header 98wherein it mixes with the heated natural gas passing into header 98 fromheader 88. The combined stream then passes into a second bank 58 of heatexchange tubes 14 connected in series and disposed within air cooler 12.A conventional temperature controller 60 is disposed within header 98 tosense the temperature of the combined stream passing therethrough.Temperature controller 60 may be any conventional pneumatic or electrictemperature controller which will generate a signal proportional to thedeviation of the temperature sensed from a desired set temperature.Control valve 56 may be any conventional automatic control valve whichwill open and close in accordance with the signal generated bytemperature controller 60.

The combined natural gas stream passes into heat exchanger tube bank 58from header 98 and is heated by the air passing through air cooler 12while cooling the air correspondingly. From heat exchanger tube bank 58,the natural gas stream passes into header 100 which is connected toheader 104. A conduit 64 is connected to conduit 38 and to header 104,and a conventional control valve 66 is disposed therein. Liqueed naturalgas from conduit 38 passes through conduit 64 and control valve 66 intoheader 104 where it is combined with the natural gas stream passing intoheader 104 from header 100. A conventional temperature controller 68 ofthe same type as described above is disposed within header 62 to sensethe temperature of the stream of natural gas therein, and to open andclose control valve 66 accordingly.

From header 104 the combined stream of natural gas passes into a thirdbank 70 of heat exchanger tubes 14 connected in series and disposedwithin air cooler 12. The combined natural gas stream passing throughbank 70 is heated by the air while the air is cooled correspondingly.From heat exchanger tube bank 70 the natural gas stream enters conduit72.

A conduit 74 is attached to conduit 72 and to conduit 42. A conventionalcontrol valve 76 is disposed within conduit 74. A conventionaltemperature controller 78 of the same type as described above isdisposed within conduit 16 to sense the temperature of the air passingtherethrough and to open and close control valve 76 accordingly.

Conduit 72 is connected to a bank 78 of heat exchanger tubes 25connected in series and disposed within heater 24. A conduit 80 isconnected to the oulet of heat exchange tube bank 78 for conducting thenatural gas to a point of distribution or use. A bypass conduit 75 isconnected between conduits 72 and 80 having a conventional control valve77 disposed therein. A conventional temperature controller 79 isconnected to conduit 80 to sense the temperature of the natural gaspassing therethrough and open and close control valve 77 accordingly.

Referring now to FIGS. 2 and 3 the apparatus of the present invention isshown mounted on a skid 82. The skid mounted apparatus basicallycomprises air inlet conduit 10, air cooler 12, turbine 18, electricgenerator 20, heater 24 and liquefied natural gas pump 34. As can beseen best in FIG. 3, heat exchange tubes 14 of air cooler 12 are groupedin three banks 50, 58 and 70, previously described. Heat exchange tubes14 in bank 50 are connected in series having an inlet 84 and an outlet86. The conduit 42 is connected to the inlet 84 of bank 50, and theoutlet 86 of bank 50 is connected to the header 88. Heat exchange tubebank 58 has an inlet 90 and an outlet 92, and heat exchange tube bank 70includes an inlet 94 and an outlet 96. The header 98 is connected to theinlet of heat exchange tube bank 58, the header is connected to theoutlet 92 of heat exchange tube bank 58 and the header 104 is connectedto the inlet 94 of heat exchange tube bank 70. Conduit 72 is connectedto the outlet 96 of heat exchange tube bank 70. Headers 88 and 98 areconnected together at the lower ends thereof by conduit 101, and headers100 and 104 are connected together at the lower ends thereof by conduit102. Conduits 54 and 56, described above are connected to headers 98 and104, respectively.

Heater 24 comprises a bank 40 of heat exchange tubes 25, connected inseries, and a bank 78 of heat exchange tubes 2S, connected in series.Heat exchange tube bank 40 includes an inlet 106 and an outlet 108. Heatexchange tube bank 78 includes an inlet 1101 and an outlet 112. Conduit32 is connected to the inlet 106 of heat exchange tube bank 40, andconduit 42 is connected to the outlet 108 of heat exchange tube bank 40.Conduit 72 is connected to the inlet 110 of heat exchange tube bank 78and conduit 80 is connected to the outlet 112 of heat exchange tube bank78.

OPERATION Referring now to FIGS. 1 through 3, atmospheric air is drawnthrough conduit into air cooler 12 wherein it is cooled from atmosphericconditions to from about 30 F. to about 40 F. The cooled air then passesthrough conduit 16 into the air intake of turbine 18. Natural gas entersturbine 18 through conduit 81 which is connected to conduit 80. Aconventional shutoff valve 83 and pressure regulator 85 are disposed inconduit 81. The natural gas and, air are combusted within turbine 18 toprovide energy for operating electric generator 20. Hot exhaust gaseshaving a temperature in the range from about 900i F. to about 1000 F.pass out of turbine 18 into conduit 22.' Conduit 22 leads the hotcombustion gases into heater 24 from where the exhaust gases are ventedto the atmosphere through conduit 26.

A stream of liquefied natural gas is pumped from storage tank 28 orother source through conduit 30 into conduit 32 by pump 34. Valve 36 inconduit 32 is adjusted so that the stream of liquefied natural .gas isdivided into two streams, one passing into conduit 38, and the otherpassing through conduit 32 into heat exchange tube bank 40 disposedwithin heater 24.

The stream' of liquefied natural gas passing through heat exchange tubebank -40 is heated and vaporized through exchange of heat with theexhaust gases passing through heater 24 on the outside of heat exchangetubes 25. The vaporized natural gas then passes into conduit 42.Temperature controller 44 senses the temperature of the vaporizednatural gas passing into conduit 42, and opens or closes valve 48accordingly. When valve 48 is opened a portion of the liquefied naturalgas bypasses heat exchange tube bank 40 and mixes with the heated andvaporized natural gas entering conduit 42 from bank 40. Upon mixing thecombined stream will be cooled and the portion of liquefied natural gasbypassed will be vaporized. In operation, temperature controller 44 isset to control the vaporized gases passing into conduit 42 at aternperature of approximately -[10 F. The temperature of the liquefiednatural gas entering conduits 32 and 38 is approximately -258 F.

The vaporized natural gas stream passes through conduit 42 and entersbank 50 of heat exchange tubes 14 disposed within air cooler 12. Heat isexchanged between the natural gas within tubes 12 and the air passing onthe outside of tubes 12 so that the air is cooled and the natural gas isheated.

As will be understood by those skilled in the art, natural gas at atemperature of |10 F. passing through heat exchange tubes 14 of bank 50will result in an initial outside heat exchange tube wall temperaturebelow 32 F. Thus, Water vapor contained within the air passing over theoutside of heat exchange tubes 12 will condense and freeze on theoutside surfaces of tubes 12. The ice formed on the outside surfaces oftubes 12 will build up and heat transferred from the inside of tubes 12to the outside will be impeded proportionately. However, the formationof ice on the outside of heat exchange tubes 12 will reach a state ofequilibrium when the ice reaches a thickness which will prevent theoutside surface of the ice from having a temperautre below 32 F. Thus,by maintaining the temperature of the natural gas passing through theinside of heat exchange tubes 12 at a temperature approaching 32 F.,such as a temperature of |10 F., only a thin layer of ice will be formedon the outside surfaces of the tubes 12 when equilibrium is reached.This thin layer will not impede the fiow of air over the tubes, orreduce the effective heat exchange area of the tubes appreciably.However, by maintaining the temperature of the natural gas passingthrough the heat exchange tubes 12 at a temperature of +10 F. or higher,the temperature of the air passing over tubes -12 can be reduced only alimited amount in a conventional single stage heat exchanger. Assumingan inlet air temperature of F., if it is attempted to reduce thetemperature of the air to from 30 F. to 40 F. with +10 F. natural gas, avery large and expensive heat exchange apparatus would be required. Thepresent invention provides a process and apparatus wherein the air iscooled in a plurality of stages thereby allowing relatively smallinexpensive heat exchange apparatus to be used while at the same timepreventing the formation of thick layers of ice on the outside of theheat exchange tubes.

This is Iaccomplished by passing natural gas at a ternperature ofapproximately {10 F. through the first bank 50 of the heat exchangertubes 12. Heat is transferred out of the, air passing over the tube bankl50 and into the natural gas, cooling the air and heating the naturalgas. The thus heated natural gas enters header #88 and passes throughconduit into header 98. In order to cool the heated natural gas streamto a temperature of approximately +10 F. a controlled quantity ofliquefied natural gas at a temperature of 258 F. is injected into header98 through conduit 54. As will be understood, the liquefied natural gaswill be vaporized when it mixes with the natural gas passing throughheader 98, and will cool the resulting combined stream of natural gas.Temperature controller y60 senses the temperature of the combined streamof natural gas and opens or closes valve 56 accordingly. That is,temperature controller 60 is set to maintain the combined stream ofnatural gas passing through header 98 at a temperature of approximately+l0 F., and controls the ow of liquefied natural gas into header 98accordingly. The thus cooled combined natural gas stream passes intobank 518 of heat exchanger tubes 14. Additional heat is transferred fromthe air passing through air cooler 12 to the natural gas stream withintube bank 58 cooling the air further. The heated natural gas streampassing out of tube bank 58 enters header 100 and passes through conduit102 into header 104. An additional quantity of liquefied natural gas isinjected into header 104 to cool the natural gas passing therethrough.Temperature controller 68 is set to control the temperature of thecombined stream of natural gas passing through header 104 at +10 F. Thethus cooled gas passes from header 104 into tube bank 70 whereinadditional heat is transferred to it from the air passing on the outsideof tube bank 70. Thus, the air passing through air cooler '12 is cooledin successive stages so that a minimum quantity of ice is formed on theoutside of heat exchanger tubes 14, and so that air cooler 12 may Iberelatively small in size and cost.

Temperature controller 78 disposed in conduit 16 senses the temperatureof the cooled air passing from air cooler 12 into turbine 18. If thetemperature of the air is too cold, temperature controller 7&8 openscontrol valve 76 causing a portion of the natural gas passing throughconduit 42 to bypass air cooler 42, thereby raising the temperature ofthe air passing through air cooler 12, and vice versa.

The stream of natural gas from -air cooler 12 passes through and mixeswith natural gas bypassed through conduit 7'4. The natural gas streamthen passes into heat exchanger tube bank 7|8 disposed in heater 24.While passing through tube bank 78, the natural gas contained therein isheated by the turbine exhaust gases passing on the outside of the tubes25 to a desired temperature. The super heated natural gas passes out oftube bank 78 into conduit `80 from where it is conducted to a point ofuse or distribution. Temperature controller 79 senses the temperature ofthe gas stream passing through conduit 80 and opens or closes bypassvalve 77 accordingly.

Thus, an improved process and apparatus for vaporizing liquefied naturalgas with turbine exhaust gases is provided wherein the turbine input airis cooled in successive stages with vaporized natural gas, therebypreventing the formation of large quantities of ice on the air coolerheat exchange tubes and permitting relatively small inexpensiveapparatus to be used.

The present invention therefore is well adapted to carry out the objectsand attain the ends and advantages mentioned, as well as those inherenttherein. While presently preferred embodiments of the invention aregiven for the purpose of disclosure, numerous changes can `be made whichwill readily suggest themselves t0 those skilled in the art, and whichare encompassed within the spirit of the invention disclosed herein.

What is claimed is:

1. In a process for vaporizing a stream of liquefied natural gas withturbine exhaust gases wherein the vaporized natural gas stream is passedthrough heat exchange tubes in heat exchange relationship with the inputair of said turbine to cool said input air, the improvementcomprisvaporizing and heating a first stream of liquified natural gaswith said turbine exhaust gases to a temperature which will bring aboutthe formation of a minimum quantity of ice on the outside surfaces ofsaid heat exchange tubes;

passing said first stream through a first bank of said heat exchangetubes so that said turbine input air is cooled and said stream isheated;

combining said first stream with a second stream of liquefied naturalgas so that the resulting stream is cooled to said temperature and saidsecond steam is vaporized;

passing said cooled combined stream through a second bank of said heatexchange tubes so that said turbine input air is cooled further; and

removing said combined stream from said process.

2. The process of claim 1 which is further characterized to include theadditional step of z heating said combined stream with said turbineexhaust gases to a desired level of super heat.

3. The process of claim 1 which is further characterized to include thesteps of 2 controlling the flow rate of said rst stream in proportion tothe temperature of said cooled turbine input air, and

controlling the flow rate of said second stream in proportion to thetemperature of said combined stream. 4. The process of claim 1 whereinis further characterized to include the additionals steps of:

combining a third stream of liquefied natural gas with said combinedstream so that the resulting stream is cooled and said third stream isvaporized; and

passing said combined cooled stream through a third bank of said heatexchanger tubes so that said turbine input air is cooled further.

5. The process of claim 4 which is further characterized to include theadditional steps of:

controlling the ow rate of said rst stream in proportion to thetemperature of said cooled turbine input air;

controlling the ow rate of said second stream in proportion to thetemperature of the combined stream comprised of said first stream andsaid second stream; and

controlling the flow rate of said third stream in pro- Cil portion tothe temperature of the combined stream comprised of said first, secondand third streams.

6. 1n apparatus for vaporizing liquefied natural gas with turbineexhaust gases which includes a turbine input air heat exchanger whereina stream of vaporized natural gas is passed through heat exchange tubesto cool said turbine input air, the improvement comprising:

means attached to said apparatus for controlling the temperature of saidstream of vaporized natural gas at a level which will bring about theformation of a minimum quantity of ice on the outside surface of saidheat exchange tubes;

said heat exchange tubes being arranged in a first bank and a secondbank, each of said banks having an inlet and outlet;

a first conduit connected to the inlet of said first bank of heatexchange tubes for conducting said stream of vaporized natural gastherethrough;

a second conduit connected to the outlet of said first bank of heatexchange tubes and connected to the inlet of said second bank of heatexchange tubes for conducting said stream of vaporized natural gastherebetween;

means attached to said second conduit for injecting a stream ofliquefied natural gas therein so that said stream of liquefied naturalgas is vaporized and the resulting combined stream of natural gas iscooled; and

a third conduit connected to the outlet of said second bank of heatexchange tubes for removing said com- `bined stream of natural gas fromsaid second bank of heat exchange tubes.

7. The apparatus of claim 6 which is further characterized to includemeans for heating said removed combined stream of natural gas to adesired level of super heat with said turbine exhaust gases.

8. The apparatus of claim 6 which is further characterized to includemeans for controlling the fiow rate of said stream of vaporized naturalgas passing into said first conduit in proportion to the temperature ofthe cooled turbine input air.

9. The apparatus of claim 6 which is further characterized to includemeans for controlling the ow rate of said stream of liquefied naturalgas injected into said second conduit in proportion to the temperatureof said combined stream of natural gas passing from said second conduitinto said second bank of heat exchange tubes.

10. In apparatus for vaporizing liquefied natural gas with turbineexhaust gases which includes a turbine input air heat exchanger whereina stream of vaporized natural gas is passed through heat exchange tubesto cool said turbine input air, the improvement comprising:

means attached to said apparatus for controlling the temperature of saidstream of vaporized natural gas at a level which will bring about theformation of a minimum of quantity of ice on the outside surface of saidheat exchange tubes;

said heat exchange tubes being arranged in a first bank, a second bank,and a third bank, each of said banks having an inlet and an outlet;

a first conduit connected to the inlet of said first bank of heatexchange tubes for conducting said stream of vaporized natural gastherethrough;

a second conduit connected to the outlet of said rst bank of heatexchange tubes and connected to the inlet of said second bank of heatexchange tubes for conducting said stream of vaporized natural gastherebetween;

means attached to said second conduit for injecting a first stream ofliquefied natural gas therein so that said first stream of liquefiednatural gas is vaporized and the resulting combined stream of naturalgas is cooled;

a third conduit connected to the outlet of said second bank of heatexchange tribes and connected to the inlet of said third bank of heatexchange tubes for conducting said combined stream of vaporized naturalgas therebetween;

means attached to said third conduit for injecting a second stream ofliquefied natural gas therein so that said second stream of liquefiednatural gas is vaporized and the resulting combined stream is cooled;

a fourth conduit connected to the outlet of said third bank of heatexchange tubes for removing said combined stream of vaporized naturalgas from said third bank of heat exchange tubes.

11. The apparatus of claim 10 which is further characterized to includemeans for heating said removed combined stream of natural gas to adesired level of super heat with said turbine exhaust gases.

12. The apparatus of claim 10 which is further characterized t0 includemeans for controlling the ow rate of said stream of vaporized naturalgas passing into said irst conduit in proportion to the temperature ofthe cooled turbine input air.

13. The apparatus of claim 10 which is further characterized to includemeans for controlling the iiow rate of said stream of liquefied naturalgas injected into said second conduit in proportion to the temperatureof said combined stream of natural gas passing from said second conduitinto said second bank of heat exchange tubes.

14. The apparatus of claim 10 which is further characterized to includemeans for controlling the ilow rate of said stream of liquefied naturalgas injected into said third conduit in proportion to the temperature ofsaid combined stream of natural gas passing from said third conduit intosaid third bank of heat exchange tubes.

References Cited UNITED STATES PATENTS 2,958,189 11/1960 Britton et al.60-39.71X 3,438,216 4/1969 Smith 62-52 ALBERT W. DAVIS, JR., PrimaryExaminer U.S. Cl. X.R.

